Lead, tin, or barium/cadmium compounds, generally in admixture with co-stabilizers, i.e., secondary stabilizers, flow promoters, and other conventional additives, are used primarily as stabilizers in the manufacture of polyvinyl chloride articles. These heavy metal stabilizers have a very satisfactory effect in practice; however, certain doubts exist concerning their use, particularly with respect to occupational physiology, i.e., toxicology. For this reason, attempts have been made for a long time to replace the normally used heavy metal stabilizers with less objectionable substances. The use of soaps of alkali metals, alkaline earth metals, or zinc in place of the heavy metal stabilizers has already been suggested. In this regard, the use of calcium soaps, which may be supplemented with co-stabilizers such as zinc stearate, imino compounds, or epoxy compounds, is preferred.
The stabilizing effect of such light metal soap systems is relatively weak in comparison to that of the heavy metal compounds. Molded articles manufactured with the use of such stabilizer systems frequently exhibit dark discolorations and have a low reserve stability. Consequently, the scope of application of such stabilizer systems is quite limited.
In U.S. Pat. No. 4,220,570 a stabilizer combination is described which contains in addition to calcium and/or zinc soaps, especially the stearates, a partial ester of pentaerythritol with a fatty acid having from 12 to 22 carbon atoms, a waxy hydrocarbon, and/or a free fatty acid having from 12 to 22 carbon atoms, as well as an antioxidant. However, this combination is not as effective as stabilizer systems based upon heavy metal compounds.
In U.S. Pat. No. 4,000,100 the use of so-called non-activated zeolite A in stabilizer systems for resin compounds based upon polyvinyl chloride, is disclosed. A significant aspect of the teaching of this reference is the realization that by incorporation of certain hydrous zeolite types in stabilizer systems, synergistic action increases with respect to thermal and light protection can be achieved. The zeolites proposed for this purpose are those of types 3A, 4A, and 5A. They are to be used with any desired inorganic, organometallic, or organic stabilizers or stabilizer components.
Co-pending U.S. patent application Ser. No. 194,851, filed Oct. 7, 1980 now U.S. Pat. No. 4,338,226, issued July 6, 1982, is directed to the stabilization of polyvinyl chloride molding mixtures by means of a complex system of primary and secondary stabilizers for polyvinyl chloride mixtures together with a powdered, crystalline, synthetic hydrous sodium aluminosilicate. More particularly, this application is directed to stabilizing molding compositions based upon polyvinyl chloride by incorporation therein, per 100 parts of polymer,
(a) from about 0.2 to 5 parts by weight of a synthetic, crystalline sodium aluminosilicate of small particle size and containing from about 13 to 25 percent by weight of water of crystallization, which has the composition EQU 0.7-1.1Na.sub.2 O.Al.sub.2 O.sub.3.1.3-2.4SiO.sub.2 PA0 with respect to the anhydrous form; PA0 (b) from about 0.05 to 1.5 parts by weight of one or more calcium salts of fatty acids with from 8 to 22 carbon atoms; PA0 (c) from about 0.05 to 0.5 parts by weight of one or more zinc salts of fatty acids with from 8 to 22 carbon atoms; PA0 (d) from about 0.2 to 2.0 parts by weight of partial esters of polyols with from 2 to 6 carbon atoms and from 2 to 6 hydroxyl groups and fatty acids with from 8 to 22 carbon atoms, which contain an average of at least one free polyol-hydroxyl group per molecule; and PA0 (e) from about 0.1 to 10 parts by weight of thioglycolic acid esters of polyols with from 2 to 6 hydroxyl groups and/or thioglycolic acid esters of monofunctional alcohols with from 8 to 22 carbon atoms. PA0 (a) from about 0.2 to 5 parts by weight of a synthetic, crystalline, powdered alkali metal aluminosilicate containing from about 13 to 25 percent by weight of water of crystallization, which has the composition EQU 0.7-1.1Me.sub.2 O.Al.sub.2 O.sub.3.1.3-2.4SiO.sub.2 PA0 with respect to the anhydrous form, Me representing an alkali metal; and PA0 (b) from about 0.1 to 5 parts by weight of at least one co-stabilizer selected from the group consisting of .beta.-diketones, .alpha.-ketoenol esters, .alpha.-acyllactones, substituted 1,4-dihydropyridine-3,5-dicarboxylic acids, and pyrrole, the pyrrole being unsubstituted or substituted in the 1-, 2-, and/or 3-position. PA0 (a) from about 0.2 to 5 parts by weight of a synthetic, crystalline, powdered alkali metal aluminosilicate containing from about 13 to 25 percent by weight of water of crystallization, which has the composition EQU 0.7-1.1Me.sub.2 O.Al.sub.2 O.sub.3.1.3-2.4SiO.sub.2 PA0 with respect to the anhydrous form, Me representing an alkali metal; and PA0 (b) from about 0.1 to 5 parts by weight of at least one co-stabilizer selected from the group consisting of .beta.-diketones, .alpha.-ketoenol esters, .alpha.-acyl-lactones, substituted 1,4-dihydropyridine-3,5-dicarboxylic acids, and pyrrole, the pyrrole being unsubstituted or substituted in the 1-, 2-, and/or 3-position.
The processing properties of polyvinyl chloride molding mixtures stabilized in the above manner compare to the properties of similar mixtures stabilized with heavy metals. This is particularly true of the initial color, the initial stability, and the residual stability of the molding compounds. However, the sulfur containing mixing component (e), the thioglycolate, can lead to problems for certain applications, for example, for packaging materials in the food sector. Since component (e) plays an important functional role in the stabilizer system mentioned in said U.S. patent application, component (e) cannot merely be deleted.